In recent years, to cope with increasing sophistication of industry, life, and administration, a demand for wireless communication systems has increased. These wireless communication systems include a wireless communication system that performs wireless communication using the frequency division multiplexing method and a wireless communication system such as a satellite communication system, for example.
It is expected that these wireless communication systems will be utilized for disaster prevention and even at a time of a disaster. For this reason, a wireless communication system is requested which is reliably operated without failure, and moreover, which is operated in a degraded operation state in the event of a failure to allow provision of minimum necessary communication.
In these communication systems, however, maintenance or repair of a wireless communication apparatus mounted on a base station or an artificial satellite, in particular, is sometimes difficult. This is because there are a lot of base stations that perform signal transmission and reception with a terminal, and due to a reason for extensive transmission of an electric wave by each base station or the like, the base station including an antenna sometimes has no choice but to be installed in a location where maintenance is difficult.
In the case of the satellite communication system, the artificial satellite is on a satellite orbit over the earth after having been launched. Thus, if a failure has occurred, repair of the wireless communication apparatus involving physical replacement such as component replacement is difficult.
Let us further consider the satellite communication system. The wireless communication apparatus mounted on the artificial satellite is requested to be operable even if power consumption is low.
It is because apparatuses mounted on the artificial satellite are configured to operate on the satellite orbit using a solar battery panel, a battery, or the like and thus to share limited electric power among the respective apparatuses mounted on the artificial satellite. It is also because, even if supply power is reduced due to degradation of the solar battery panel or at a time of a failure of an electric power system, continuation of a communication service is desirable. In this way, even if power consumption is low, the wireless communication apparatus mounted on the artificial satellite is requested to operate as normally as possible, as a wireless communication apparatus.
As an example of the wireless communication apparatus mounted on the artificial satellite that is a target of the requests as mentioned above, there is a digital channelizer (see Patent Literature 1, for example). The digital channelizer is a satellite relay capable of flexibly accommodating a communication need or a change in demand after launching of the artificial satellite. There is also digital beam forming (DBF) (see Patent Literature 2, for example) capable of flexibly performing beam formation by performing digital signal processing when the beam formation is performed using an array antenna or the like.
An apparatus such as the digital channelizer or an apparatus for the DBF or the like has a digital signal processing mechanism that digitizes an analog signal and performs a frequency division or multiplexing process, a DBF operation, switching, and so forth for a digital signal. Then, these apparatuses such as the digital channelizer and the apparatus for the DBF or the like accommodate the need and the change in demand by utilizing flexibility of digital signal processing.
A description will be given about a case where the wireless relay including the digital channelizer is mounted on the artificial satellite and the satellite communication system is implemented, using the frequency division multiplexing method, for example.
In the case of such a satellite communication system, communication between the artificial satellite and a ground station in one hop is possible. Further, the satellite communication system has flexibility capable of readily performing addition or deletion of a service to a user.
However, a demand for provision of a service to a larger number of users and provision of a high-speed communication service by communication band expansion is increasing for such a satellite communication system. Communication capacities and signal processing scales of these wireless communication apparatuses such as the digital channelizer and the apparatus for the DBF therefore tend to increase.
To cope with the requests for the wireless communication apparatus as mentioned above, technologies in Patent Literatures 1 and 2 are disclosed.
Patent Literature 1 discloses an embodiment including the digital channelizer, a digital switch matrix, and a digital combiner as a digital payload. Further, a digital payload having three multi-port DSP processing slices including functions of these apparatuses is disclosed.
In a communication system, it is a common practice to set a part of all frequency bands that can be used by the system to be unused and to perform normal operation using a remainder of the frequency bands.
Patent Literature 2 discloses an embodiment in which this frequency band set to be unused is focused on to reduce power consumption of the wireless communication apparatus.